U.S. patent number 7,179,860 [Application Number 11/033,461] was granted by the patent office on 2007-02-20 for crosslinked polymer electrolyte membranes for heat, ion and moisture exchange devices.
This patent grant is currently assigned to Liwei Cao, Scott G. Ehrenberg, Joseph M. Serpico. Invention is credited to Liwei Cao, Scott G. Ehrenberg, Joseph M. Serpico.
United States Patent |
7,179,860 |
Cao , et al. |
February 20, 2007 |
Crosslinked polymer electrolyte membranes for heat, ion and
moisture exchange devices
Abstract
An organic-inorganic hybrid is derived from combining at least
one inorganic alkoxide and a hydrogenated sulfonated block
copolymer containing a controlled distribution copolymer block of a
conjugated diene and a mono alkenyl arene, where the controlled
distribution copolymer block has terminal regions that are rich in
conjugated diene units and a center region that is rich in mono
alkenyl arene units. The inorganic alkoxide may be an alkoxysilane
compound or composition.
Inventors: |
Cao; Liwei (Lutz, FL),
Ehrenberg; Scott G. (New Port Richey, FL), Serpico; Joseph
M. (Palm Harbor, FL) |
Assignee: |
Cao; Liwei (FL)
Ehrenberg; Scott G. (New Port Richey, FL)
Serpico; Joseph M. (Palm Harbor, FL)
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Family
ID: |
34990919 |
Appl.
No.: |
11/033,461 |
Filed: |
January 11, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050215728 A1 |
Sep 29, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/US04/30936 |
Sep 22, 2004 |
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10268039 |
Oct 9, 2002 |
6841601 |
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10098928 |
Mar 13, 2002 |
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60505283 |
Sep 23, 2003 |
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60327746 |
Oct 9, 2001 |
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60275459 |
Mar 13, 2001 |
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Current U.S.
Class: |
524/575; 524/261;
524/264; 524/398; 524/413 |
Current CPC
Class: |
C08F
8/42 (20130101); C08F 8/42 (20130101); C08F
297/00 (20130101) |
Current International
Class: |
C08L
9/06 (20060101); C08K 3/10 (20060101) |
Field of
Search: |
;524/575,398,261,264,413 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wu; David W.
Assistant Examiner: Lee; Rip
Attorney, Agent or Firm: Heslin Rothenberg Farley &
Mesiti, P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. non-provisional
application Ser. No. 10/268,039, filed on Oct. 9, 2002, now U.S.
Pat. No. 6,841,601, and copending International application number
PCT/US04/30936, filed on Sep. 22, 2004. U.S. Non-provisional
application, Ser. No. 10/268,039, filed on Oct. 9, 2002, claims
priority from U.S. provisional application, Ser. No. 60/327,746,
filed Oct. 9, 2001, now abandoned and U.S. non-provisional
application, Ser. No. 10/098,928, now abandoned filed Mar. 13,
2002, which claimed priority from U.S. provisional applications
60/275,459, filed Mar. 13, 2001, and 60/327,746, filed Oct. 9,
2001. International application number PCT/US04/30936, filed on
Sep. 22, 2004, claims priority from U.S. provisional application
Ser. No. 60/505,283, filed Sep. 23, 2003.
Claims
The invention claimed is:
1. An organic-inorganic hybrid derived from combining at least one
inorganic alkoxide and a sulfonated hydrogenated block copolymer
having the general configuration A-B, A-B-A, (A-B)n, (A-B-A)n,
(A-B-A)nX, (AB)nX or mixtures thereof, where n is an integer from 2
to 30, and X is coupling agent residue and wherein: a. prior to
hydrogenation each A block is a mono alkenyl arene polymer block
and each B block is a controlled distribution copolymer block of at
least one conjugated diene and at least one mono alkenyl arene; b.
subsequent to hydrogenation 0 10% of the arene double bonds have
been reduced, and at least about 90% of the conjugated diene double
bonds have been reduced; c. each A block having a number average
molecular weight between 3,000 and 60,000 and each B block having a
number average molecular weight between 30,000 and 300,000; d. each
B block comprises terminal regions adjacent to the A blocks that
are rich in conjugated diene units and one or more regions not
adjacent to the A blocks that are rich in mono alkenyl arene units;
e. the total amount of mono alkenyl arene in the hydrogenated block
copolymer is 20 percent weight to 80 percent weight; f. the weight
percent of mono alkenyl arene in each B block is between 10 percent
and 75 percent; and g. at least 25% of the aromatic rings of the
alkenyl arene are sulfonated.
2. An organic-inorganic hybrid according to claim 1 wherein the
mono alkenyl arene is styrene and the conjugated diene is selected
from the group consisting of isoprene and butadiene.
3. An organic-inorganic hybrid according to claim 1 wherein the
conjugated diene is butadiene, and wherein 20 to 80 mol percent of
the condensed butadiene units in block B have 1,2-configuration
prior to hydrogenation.
4. An organic-inorganic hybrid according to claim 1 wherein block B
has a styrene blockiness index of less than 40 percent.
5. An organic-inorganic hybrid according to claim 1 wherein each
block B has a center region with a minimum ratio of butadiene units
to styrene units.
6. An organic-inorganic hybrid according to claim 1 wherein the
mono alkenyl arene is styrene, and wherein the weight percentage of
styrene in block B is between 20 percent and 70 percent, and the
styrene blockiness index of is less than 10 percent, the styrene
blockiness index being the proportion of styrene units in the block
B having two styrene neighbors on the polymer chain.
7. An organic-inorganic hybrid according to claim 1 wherein the
weight percentage of styrene in the block copolymer is between 60
and 80 weight percent and the molecular weight of the A blocks are
between 10.000 and 35,000.
8. An organic-inorganic hybrid according to claim 1 wherein between
25 and 90 percent of the aromatic rings have a sulfonic acid or
sulfonate group.
9. An organic-inorganic hybrid according to claim 1 wherein from 25
percent to 70 percent of the aromatic rings have a sulfonic acid or
sulfonate group.
10. An organic-inorganic hybrid according to claim 1 wherein from
25 percent to 50 percent of the aromatic rings have a sulfonic acid
or sulfonate group.
11. An organic-inorganic hybrid according to claim 1, wherein said
inorganic alkoxide has the formula:
R.sup.1.sub.mMR.sup.2.sub.nR.sup.3.sub.pR.sup.4.sub.(4-m-n-p)
wherein M is Si, Ti, Zr, or mixtures thereof; R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are independently alkyl, substituted alkyl,
alkenyl, aryl, acyloxy, alkoxy, halo, amino, mercapto, or epoxy; m,
n and p are independently 0, 1, 2, 3 or 4; and at least one of
R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is alkoxy.
12. An organic-inorganic hybrid according to claim 11, wherein M is
Si or Zr.
13. An organic-inorganic hybrid according to claim 11, wherein M is
Si.
14. An organic-inorganic hybrid according to claim 11, wherein said
inorganic alkoxide is vinyltriethoxysilane or
vinyltrimethoxysilane.
15. An organic-inorganic hybrid according to claim 11, wherein
R.sup.1 is alkyl, substituted alkyl, alkenyl, acyloxy, halo, amino,
mercapto, or epoxy; R.sup.2 is alkyl, substituted alkyl, alkenyl,
acyloxy, alkoxy, halo, amino, mercapto, or epoxy; R.sup.3 and
R.sup.4 are alkoxy; and m is 1.
16. An organic-inorganic hybrid according to claim 11, wherein
R.sup.1 is alkyl, substituted alkyl, alkenyl, acyloxy, halo, amino,
mercapto, or epoxy; R.sup.2, R.sup.3 and R.sup.4 are alkoxy; and m
is 1.
17. A membrane for transferring heat, ions, moisture, polar liquids
and/or polar gases, said membrane comprising the organic-inorganic
hybrid of claim 1.
18. An organic-inorganic hybrid according to claim 11, wherein said
sulfonated hydrogenated block copolymer comprises from 20 weight
percent to 80 weight percent styrene.
19. An organic-inorganic hybrid according to claim 11, comprising
from 25 mole percent to 80 mole percent of units derived from
styrene sulfonate.
Description
BACKGROUND OF THE INVENTION
A unitary humidity exchange cell (or HUX), as the name implies, is
an element of a device that is capable of transferring water or
other highly polar liquid or gas from one side of the cell to the
other by action of a difference in some quantity or gradient across
said cell. A key operational characteristic of the HUX cell is that
a difference of some intensive or extensive property of the system
(relative to the surrounding) leads to a gradient change of said
property to effect mass transfer of water or some other highly
polar liquid or gas from one side of the membrane to the other with
or without an accompanying flow of electrons, protons, ions or
molecules other than said water or other highly polar liquid or
gas. It is under the influence of this property that exchange in
liquid water or some other highly polar liquid or gas occurs across
the permaselective membrane. This transfer of water or some other
highly polar liquid or gas may or may not be accompanied by
evaporation of said water or other highly polar liquid or gas into
(or from) the stream by the absorption of heat or adiabatically or
by some other thermodynamic means; for example the condensation or
evaporation of liquid water or some other highly polar liquid or
gas or the simple diffusion of water or some other highly polar
liquid or gas into a pure liquid stream. A finite gradient across
the membrane must exist in some quantity; examples are vapor
pressure, osmotic or hydrostatic pressure, chemical,
thermochemical, electrochemical, magnetochemical potential, as well
as thermal (temperature or heat content), electric,
electromagnetic, thermoelectric, or electrothermal potential
difference. There must be at least two streams, one supplied to
each surface of said membrane by some means either as a liquid or
vapor flow each of which differs in at least one identical property
of the system. The system attempts to reach a thermodynamic
equilibrium by transporting water or some other highly polar liquid
or gas from one stream to the other. The orientation of the streams
to one another is considered arbitrary for the invention; these may
be counter flow, coflow, crossflow, mixed flow or any other
geometric arrangement of one or more streams. Water or some other
highly polar liquid or gas transport (e.g. hydrodynamic,
electrohydrodynamic, magnetohydrodynamic, diffusion, migration, or
convection) occurs until the imposed gradient can no longer meet
the physicochemical constraints of the system required to sustain
the motion. In many cases, the exchange of water or some other
highly polar liquid or gas between the streams is slow, but this
may be due to some other limiting factor, such as, boundary layer
effects, concentration polarization, hydrostatic pressure lag or
gravity, surface tension effects, and convective or frictional
effects. However, once these engineering design or system effects
are minimized, inevitably, the exchange or transport of water or
some other highly polar liquid or gas is rate-limiting if the
permeability of the membrane to water or some other highly polar
liquid or gas is poor. Hence, an important object of the invention
is that hydrophilic polymer membrane has high permeability to water
or some other highly polar liquid or gas; more than necessary for
most applications. The hydrophilic polymer membrane (or
formulation) must be mechanically supported and there must be means
to supply the two streams to said surfaces. A second object of the
invention is that the three sub-elements be fabricated as one unit
by conventional means at low cost. This requires that the
hydrophilic polymer wet the support, achieve intimate contact and
demonstrate exceptional adhesion to it. Therefore, a third object
of the invention is that the support be a polyolefin or blend
thereof such that one component of said hydrophilic polymer is
similar in chemical structure to one component of the support.
HUX cell design is general in that water (liquid or vapor) or other
highly polar material (liquid or vapor) can be transferred between
any two fluids. Examples of applications are per-vaporation,
humidification and dehumidification of fuel cell streams in stacks
and devices, drying gases at pressure, tertiary oil recovery,
process control for chemical manufacture of chemicals for which
water is a reactant, isolation of minerals from mining fluids,
industrial separation of oil-water emulsions, microfiltration and
ultrafiltration of colloidal suspensions and biological or organic
macromolecules for purification, maintaining water content of
methanol in direct methanol fuel cells, reverse osmosis for
isolation of fresh water from brine, electrolysis cells, dialysis,
electro-dialysis, piezo-dialysis, electro-osmosis and chloro-alkali
cells.
SUMMARY OF THE INVENTION
The present invention relates to cells for transferring heat, ions
and/or moisture between a first fluid and a second fluid. Such a
cell comprises at least one hydrophilic organic-inorganic hybrid
membrane, disposed between at least one first chamber for flow of
the first fluid therethrough and at least one second chamber for
flow of the second fluid therethrough; whereby heat and moisture is
transferable between the first fluid and second fluid via the
membrane. The membranes are prepared from an organic-inorganic
hybrid derived from combining at least one inorganic alkoxide and a
hydrogenated sulfonated block copolymer. The cell may additionally
include at least one spacer disposed on a surface of the membrane.
The spacer(s) may have a dimension normal to the surface of the
membrane corresponding to a height of the first chamber; the
longitudinal axis of the at least one spacer may be oriented
parallel to a direction of flow of the first fluid in the first
chamber. The direction of flow of the first fluid in the first
chamber may be orthogonal to a direction of flow of the second
fluid in the second chamber, or it may be opposite to it. In some
embodiments, a plurality of synthetic polymer ribs are used as
spacers; in others, the spacer is merely a bead of an adhesive
composition; in still others, the spacer is a corrugated sheet
composed of paper or plastic. The invention also relates to cells
containing a plurality of hydrophilic organic-inorganic hybrid
membranes, and a plurality of alternating first chambers and second
chambers, each separated by such a membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a hydrophilic organic-inorganic hybrid membrane for
use in a humidity exchange cell according to present invention.
FIG. 2 is a partially exploded view of a humidity exchange cell
according to the present invention.
FIG. 3 is a graph showing high heat and water transfer using a
humidity exchange cell according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a single hydrophilic organic-inorganic hybrid membrane
10 for use in a humidity exchange cell according to the present
invention. The membrane includes a continuous film of a
humidity-conducting polymer 12 bonded to a reinforcing substrate 14
in the form of a cross-laid mesh or netting. Reinforcing substrate
14 strengthens the membrane so it can be handled, and allows the
membrane to withstand pressure differentials without deflecting. As
shown in FIG. 1, there are spacers, ribs or ridges 16 adhered to
the surface of membrane 10 and running in one direction. The other
side of the membrane is a smooth surface of humidity-conducting
polymer 12. The height of spacer 16 sets the layer-to-layer
spacing. Air channels in the humidity exchange cell are formed by
spacers 16 when they rest against the smooth surface of the
membrane that is placed on top of it.
The humidity-conducting polymer is preferably an organic-inorganic
hybrid. In these hybrid materials, the organic (polymer) and
inorganic components are combined at the molecular level; the
hybrids may be derived from a reaction between the polymer and the
inorganic alkoxide, resulting in a polymer matrix nanocomposite.
The presence of a finely dispersed inorganic oxide gel/polymer
network provides good mechanical strength, extraordinary thermal
stability, dimensional stability, good transport properties, ionic
conductivity and/or permeability and permeselectivity.
In particular, the hybrid is prepared by combining a hydrogenated
sulfonated block copolymer having a controlled distribution
copolymer block of a conjugated diene and a mono alkenyl arene with
an inorganic alkoxide having the formula:
R.sup.1.sub.mMR.sup.2.sub.nR.sup.3.sub.pR.sup.4.sub.(4-m-n-p)
wherein M is Si, Ti, Zr, or mixtures thereof; R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are independently alkyl, substituted alkyl,
alkenyl, acyloxy, alkoxy, halo, amino, mercapto, or epoxy; m, n and
p are independently 0, 1, 2, 3 or 4; and at least one of R.sup.1,
R.sup.2, R.sup.3 and R.sup.4 is alkoxy.
In some embodiments, M may be limited to Si or Zr; Si and Zr are
particularly useful. Examples of specific inorganic alkoxides
include tetraethylorthosilicate, vinyltriethoxysilane,
vinyltrimethoxysilane, and zirconium bis(diethyl
citrato)dipropoxide.
The organic-inorganic hybrid materials may be prepared by using a
sol-gel type process, which is an acid or base-catalyzed
hydrolysis-condensation reaction of inorganic alkoxides. Where only
the inorganic alkoxide is present, the reaction typically is run in
a solvent containing water, and proper drying of the swollen gel
produces an inorganic oxide glass. For example, where the inorganic
alkoxide is an alkoxy silane, polysilicates typically grow in
molecular weight and chain length within the polymer until most or
all of the alkoxy groups are removed and a nonlinear network of
Si--O--Si remains. Stable condensation products are also form with
other oxides such as those of aluminum, zirconium, tin, and nickel.
Where at least one of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is a
nonhydrolyzable organic functional group, typically vinyl, amino,
chloro, epoxy, mercapto, the functional group may attach to the
polymer while the alkoxy group(s) may attach to silicon. As the
hydrolysis reaction progresses, the inorganic alkoxides may
condensation to form oligomers, and then polysilcates.
Inorganic alkoxides include tetralkoxysilanes [Si(OR).sub.4],
tetraalkyl titanates [Ti(OR).sub.4] and tetraalkyl zirconates
[Zr(OR).sub.4], where R is alkyl, particularly, methyl, ethyl,
propyl, isopropyl, n-butyl, or t-butyl, and organosilanes
[R.sub.nSiX.sub.(4-n)], organic titanates [R.sub.nTiX.sub.(4-n)],
organic zirconates [R.sub.nZrX.sub.(4-n)]. The most common alkoxy
groups are methoxy, and ethoxy. Other inorganic alkoxides that may
be useful in hydrophilic organic-inorganic hybrids used as heat,
ion and moisture tranfer membranes are based on aluminum, tin and
boron.
A humidity-conducting polymer for use in a humidity exchange cell
of the present invention typically contains at least 20 weight % of
residues derived from styrene. More preferably, the copolymer
contains from 20 to 80 weight % styrene, and most preferably, about
65 weight % styrene. The range of weight average molecular weight
(M.sub.w) of the polymer of the invention is from about 20,000
grams/mole to about 1,000,000 grams/mole, and preferably from about
50,000 grams/mole to 900,000 grams/mole. The sulfonated polymer
used for the membranes of the present invention are preferably
water-insoluble. Water-insoluble is defined as having a solubility
of less than 0.5 grams of polymer in 100 grams of water at
100.degree. C.
The polymer in the organic-inorganic hybrid is preferably derived
from an at least partially sulfonated copolymer that possesses a
low equivalent weight, from 1000 down to 100, preferably 700 down
to 400 and most preferably 690 down to 520. Partially sulfonated
styrene-olefin copolymers are generally preferred. Specifically,
the polymer is a hydrogenated sulfonated block copolymer having
controlled distribution blocks.
"Controlled distribution" is defined as referring to a molecular
structure having the following attributes: (1) terminal regions
adjacent to the mono alkenyl arene homopolymer ("A") blocks that
are rich in (i.e., having a greater than average amount of)
conjugated diene units; (2) one or more regions not adjacent to the
A blocks that are rich in (i.e., having a greater than average
amount of) mono alkenyl arene units; and (3) an overall structure
having relatively low blockiness. For the purposes hereof, "rich
in" is defined as greater than the average amount, preferably
greater than 5% the average amount. This relatively low blockiness
can be shown by either the presence of only a single glass
transition temperature ("Tg,") intermediate between the Tg's of
either monomer alone, when analyzed using differential scanning
calorimetry ("DSC") thermal methods or via mechanical methods, or
as shown via proton nuclear magnetic resonance ("H-NMR") methods.
The potential for blockiness can also be inferred from measurement
of the UV-visible absorbance in a wavelength range suitable for the
detection of polystyryllithium end groups during the polymerization
of the B block. A sharp and substantial increase in this value is
indicative of a substantial increase in polystyryllithium chain
ends. In this process, this will only occur if the conjugated diene
concentration drops below the critical level to maintain controlled
distribution polymerization. Any styrene monomer that is present at
this point will add in a blocky fashion. The term "styrene
blockiness", as measured by those skilled in the art using proton
NMR, is defined to be the proportion of S units in the polymer
having two S nearest neighbors on the polymer chain. The styrene
blockiness is determined after using H-1 NMR to measure two
experimental quantities as follows: First, the total number of
styrene units (i.e. arbitrary instrument units which cancel out
when ratioed) is determined by integrating the total styrene
aromatic signal in the H-1 NMR spectrum from 7.5 to 6.2 ppm and
dividing this quantity by 5 to account for the 5 aromatic hydrogens
on each styrene aromatic ring. Second, the blocky styrene units are
determined by integrating that portion of the aromatic signal in
the H-1 NMR spectrum from the signal minimum between 6.88 and 6.80
to 6.2 ppm and dividing this quantity by 2 to account for the 2
ortho hydrogens on each blocky styrene aromatic ring. The
assignment of this signal to the two ortho hydrogens on the rings
of those styrene units which have two styrene nearest neighbors was
reported in F. A. Bovey, High Resolution NMR of Macromolecules
(Academic Press, New York and London, 1972), chapter 6. The styrene
blockiness is simply the percentage of blocky styrene to total
styrene units: Blocky %=100 times (Blocky Styrene Units/Total
Styrene Units) Expressed thus, Polymer-Bd-S--(S)n-S-Bd-Polymer,
where n is greater than zero is defined to be blocky styrene. For
example, if n equals 8 in the example above, then the blockiness
index would be 80%. It is preferred that the blockiness index be
less than about 40. For some polymers, having styrene contents of
ten weight percent to forty weight percent, it is preferred that
the blockiness index be less than about 10.
This controlled distribution structure is very important in
managing the strength and Tg of the resulting copolymer, because
the controlled distribution structure ensures that there is
virtually no phase separation of the two monomers, i.e., in
contrast with block copolymers in which the monomers actually
remain as separate "microphases", with distinct Tg's, but are
actually chemically bonded together. This controlled distribution
structure assures that only one Tg is present and that, therefore,
the thermal performance of the resulting copolymer is predictable
and, in fact, predeterminable. Furthermore, when a copolymer having
such a controlled distribution structure is then used as one block
in a di-block, tri-block or multi-block copolymer, the relatively
higher Tg made possible by means of the presence of an
appropriately-constituted controlled distribution copolymer region
will tend to improve flow and processability. Modification of
certain other properties is also achievable.
The controlled distribution copolymer block has two distinct types
of regions--conjugated diene rich regions on the end of the block
and a mono alkenyl arene rich region near the middle or center of
the block. What is desired is a mono alkenyl arene/conjugated diene
controlled distribution copolymer block, wherein the proportion of
mono alkenyl arene units increases gradually to a maximum near the
middle or center of the block and then decreases gradually until
the polymer block is fully polymerized. This structure is distinct
and different from the tapered and/or random structures discussed
in the prior art.
Anionic, solution copolymerization to form the controlled
distribution copolymers can be carried out using, to a great
extent, known and previously employed methods and materials. In
general, the copolymerization is attained anionically, using known
selections of adjunct materials, including polymerization
initiators, solvents, promoters, and structure modifiers, but as a
key feature, in the presence of a certain distribution agent. Such
distribution agent is, in preferred embodiments, a non-chelating
ether. Examples of such ether compounds are cyclic ethers such as
tetrahydrofuran and tetrahydropyran and aliphatic monoethers such
as diethyl ether and dibutyl ether. In some cases, particularly
where the vinyl content of the conjugated diene is to be over 50%,
it may be necessary to use a chelating agent, including dialkyl
ethers of ethylene glycol and aliphatic polyethers such as
diethylene glycol dimethyl ether and diethylene glycol diethyl
ether. Other distribution agents include, for example,
ortho-dimethoxybenzene or "ODMB", which is sometimes referred to as
a chelating agent. Preferably the ether is an aliphatic monoether,
and more preferably diethyl ether. Such copolymerization can be
conducted as a batch, semi-batch, or continuous preparation, with
batch being most preferred, but regardless, it is important that
the randomization agent be present in the selected solvent prior to
or concurrent with the beginning of the copolymerization
process.
The introduction of the distribution agent counteracts the
preference of the growing chain end to attach to one monomer over
another. For example, in the case of styrene and a diene, the
preference would be toward the diene. This distribution agent
operates to promote more efficient "controlled distribution"
copolymerization of the two monomers because the living chain end
"sees" one monomer approximately as easily as it "sees" the other.
The polymerization process is thereby "tuned" to allow
incorporation of each of the monomers into the polymer at nearly
the same rate. Such a process results in a copolymer having no
"long runs" of either of the monomer components--in other words, a
controlled distribution copolymer as defined hereinabove. In the
preferred process, the mono alkenyl arene monomer will be nearly
consumed by the time that the slow addition of the second aliquot
of diene is complete, so that the polymerization ends rich in the
conjugated diene. Short blocks of the conjugated diene monomer may
be formed throughout the polymerization, but blocks of the mono
alkenyl arene monomer are only formed when the concentration of the
conjugated diene monomer becomes quite low. Under the preferred
conditions, the cumulative percentage of the mono alkenyl arene
monomer in the B block peaks at about 40% 60% overall conversion,
but only exceeds the final value by about 25% 30%. The result of
this relatively uniform distribution of monomers is a product
having a single Tg, which is a weighted average of the Tg values of
the two corresponding homopolymers.
As noted above, the distribution agent is preferably a
non-chelating ether. By "non-chelating" is meant that such ethers
will not chelate with the growing polymer, that is to say, they
will not form a specific interaction with the chain end, which is
derived from the initiator compound (e.g., lithium ion). Because
the non-chelating ethers used in the present invention operate by
modifying the polarity of the entire polymerization charge, they
are preferably used in relatively large concentrations. Where
diethyl ether, which is preferred, is selected, it is preferably at
a concentration from about 0.5 to about 10 percent, preferably
about 1 to about 10 percent, by weight of the polymerization charge
(solvent and monomers), and more preferably from about 3 to about 6
percent by weight. Higher concentrations of this monoether can
alternatively be used, but appear to increase cost without added
efficacy. When the distribution agent is ODMB, the amount used is
typically about 20 to about 400 parts by million weight ("PPMW"),
based on the total reactor contents, preferably about 20 to about
40 PPMW for low vinyl products and about 100 to 200 PPMW for higher
vinyl products.
The microstructure or vinyl content of the conjugated diene in the
controlled distribution copolymer block is typically controlled.
The term "vinyl content" refers to the fact that a conjugated diene
is polymerized via 1,2-addition (in the case of butadiene--it would
be 3,4-addition in the case of isoprene). Although a pure "vinyl"
group is formed only in the case of 1,2-addition polymerization of
1,3-butadiene, the effects of 3,4-addition polymerization of
isoprene (and similar addition for other conjugated dienes) on the
final properties of the block copolymer will be similar. The term
"vinyl" refers to the presence of a pendant vinyl group on the
polymer chain. When referring to the use of butadiene as the
conjugated diene, it is preferred that about 20 to about 80 mol
percent of the condensed butadiene units in the copolymer block
have 1,2 vinyl configuration as determined by proton NMR analysis.
For selectively hydrogenated block copolymers, preferably about 30
to about 70 mol percent of the condensed butadiene units should
have 1,2 configuration. For unsaturated block copolymers,
preferably about 20 to about 40 mol percent of the condensed
butadiene units should have 1,2-vinyl configuration. This is
effectively controlled by varying the relative amount of the
distribution agent. As will be appreciated, the distribution agent
serves two purposes--it creates the controlled distribution of the
mono alkenyl arene and conjugated diene, and also controls the
microstructure of the conjugated diene. Suitable ratios of
distribution agent to lithium are disclosed and taught in U.S. Pat.
No. Re 27,145, which disclosure is incorporated by reference.
The solvent used as the polymerization vehicle may be any
hydrocarbon that does not react with the living anionic chain end
of the forming polymer, is easily handled in commercial
polymerization units, and offers the appropriate solubility
characteristics for the product polymer. For example, non-polar
aliphatic hydrocarbons, which are generally lacking in ionizable
hydrogens make particularly suitable solvents. Frequently used are
cyclic alkanes, such as cyclopentane, cyclohexane, cycloheptane,
and cyclooctane, all of which are relatively non-polar. Other
suitable solvents will be known to one skilled in the art and can
be selected to perform effectively in a given set of process
conditions, with temperature being one of the major factors taken
into consideration.
Starting materials for preparing the controlled distribution
copolymers include the initial monomers. The alkenyl arene can be
selected from styrene, alpha-methylstyrene, para-methylstyrene,
vinyl toluene, vinyinaphthalene, and para-butyl styrene or mixtures
thereof. Of these, styrene is most preferred and is commercially
available, and relatively inexpensive, from a variety of
manufacturers. The conjugated dienes for use herein are
1,3-butadiene and substituted butadienes such as isoprene,
piperylene, 2,3-dimethyl-1,3-butadiene, and 1-phenyl-1,3-butadiene,
or mixtures thereof. Of these, 1,3-butadiene is most preferred. As
used herein, and in the claims, "butadiene" refers specifically to
"1,3-butadiene".
Other important starting materials for anionic copolymerizations
include one or more polymerization initiators. In the present
invention such include, for example, alkyl lithium compounds and
other organolithium compounds such as s-butyllithium,
n-butyllithium, t-butyllithium, amyllithium and the like, including
di-initiators such as the di-sec-butyl lithium adduct of
m-diisopropenyl benzene. Other such di-initiators are disclosed in
U.S. Pat. No. 6,492,469. Of the various polymerization initiators,
s-butyllithium is preferred. The initiator can be used in the
polymerization mixture (including monomers and solvent) in an
amount calculated on the basis of one initiator molecule per
desired polymer chain. The lithium initiator process is well known
and is described in, for example, U.S. Pat. Nos. 4,039,593 and Re.
27,145, which descriptions are incorporated herein by
reference.
Polymerization conditions to prepare the novel copolymers are
typically similar to those used for anionic polymerizations in
general. In the present invention polymerization is preferably
carried out at a temperature of from about -30.degree. to about
150.degree. C., more preferably about 10.degree. to about
100.degree. C., and most preferably, in view of industrial
limitations, about 30.degree. to about 90.degree. C. It is carried
out in an inert atmosphere preferably nitrogen, and may also be
accomplished under pressure within the range of from about 0.5 to
about 10 bars. This copolymerization generally requires less than
about 12 hours, and can be accomplished in from about 5 minutes to
about 5 hours, depending upon the temperature, the concentration of
the monomer components, the molecular weight of the polymer and the
amount of distribution agent that is employed.
As discussed above, an important discovery is the control of the
monomer feed during the polymerization of the controlled
distribution block. To minimize blockiness, it is desirable to
polymerize as much of the styrene as possible in the presence of
butadiene. Towards that end, a preferred process adds the styrene
charge as quickly as possible, while adding the butadiene slowly,
so as to maintain a concentration of no less than about 0.1% wt of
butadiene for as long as possible, preferably until the styrene is
nearly exhausted. If the butadiene falls below this level, there is
a risk that a styrene block will form at this point. It is
generally undesirable to form a styrene block during the butadiene
charge portion of the reaction.
In a two-reactor polymerization scheme, this is most readily
accomplished by adding about 80 to 100 percent of the mono alkenyl
arene to the second reactor, along with about 10 to about 60
percent of the conjugated diene. The monomers are then caused to
start polymerization via transfer of the living polymer from the
first reactor. After about 5 to 60 mol percent of the monomers have
polymerized, the remaining portion of the mono alkenyl arene (if
any) is added and the remaining conjugated diene monomer is added
at a rate that maintains the concentration of the conjugated diene
monomer at no less than about 0.1% weight. The rate of diene
monomer addition will be determined by the styrene content of the
midblock, the reaction temperature and the type and concentration
of the distribution control agent used. Reaction rates are
relatively fast in the presence of 6% 10% diethyl ether. In this
system, the diene is typically charged over 15 to 60 minutes. Rates
for both monomers are slower in the presence of 0.5% 1% diethyl
ether or 35 40 PPM o-dimethoxybenzene. In this solvent system, it
is more typical to add the diene over 60 to 90 minutes. The higher
the midblock styrene, the more advantageous it is to add the diene
slowly. If the polymer is to be prepared in a fully sequential
process, it is preferable to ensure that the butadiene addition
continues until about 90% of the monomers in block B1 have been
polymerized, and the percentage of the mono alkenyl arene monomer
in the non-reacted monomer pool has been reduced to less than 20%
weight, preferably less than 15% weight. In this way the formation
of styrene blocks is prevented throughout the majority of the
polymerization and there is sufficient conjugated diene left at the
end of the polymerization to ensure that the terminal region of the
B1 block is richer in the diene monomer. The resulting polymer
block has diene rich regions near the beginning and the end of the
block and an arene rich region near the center of the block. In
products of the preferred process, typically the first 15 to 25%
and the last 75 to 85% of the block are diene rich, with the
remainder considered to be arene rich. The term "diene rich" means
that the region has a measurably higher ratio of diene to arene
than the center region. Another way to express this is the
proportion of mono alkenyl arene units increases gradually along
the polymer chain to a maximum near the middle or center of the
block and then decreases gradually until the polymer block is fully
polymerized. In a preferred embodiment, all of the mono alkenyl
arene and about 10 to 20 percent of the conjugated diene are
charged to the reactor, and the remainder of the conjugated diene
is added after about 5 to about 10 percent of the original monomers
have polymerized.
It is typically possible to achieve the desired distribution of the
arene monomer in the final product using the process described
above if fairly high levels of the distribution control agent are
used. At higher midblock styrene levels and low levels of the
distribution control agent, some blockiness is unavoidable. It is
preferable to prepare these products by coupling. This insures that
any blocky styrene that is formed is located at some distance from
the endblocks. When polymers are prepared by coupling, it is
preferable to reserve 5% to 10% of the diene monomer, and add this
charge once the polymerization of the arene monomer is complete.
This ensures that all of the chains end in a diene unit. The living
diene chain ends generally react more efficiently with coupling
agents.
If the products are being prepared in a single reactor process in
which all of the B1 monomer is charged to a reactor containing the
living A block, it is preferable to start the diene monomer
addition about 1 minute before starting the arene monomer addition.
It is also preferable to charge both monomers rapidly at first and
then decrease the diene addition rate once the majority of the
arene monomer has been added. This process ensures that the initial
region of the B1 block will be rich in the diene monomer, and
builds a large enough pool to avoid becoming starved in the diene
monomer early in process step. As discussed above, the optimal
rates will depend on the styrene content of the midblock, the
reaction temperature and the type and concentration of the
distribution control agent used.
For the controlled distribution or B block the weight percent of
mono alkenyl arene in each B block is between about 10 weight
percent and about 75 weight percent, preferably between about 25
weight percent and about 50 weight percent for selectively
hydrogenated polymers.
As used herein, "thermoplastic block copolymer" is defined as a
block copolymer having at least a first block of one or more mono
alkenyl arenes, such as styrene and a second block of a controlled
distribution copolymer of diene and mono alkenyl arene. The method
to prepare this thermoplastic block copolymer is via any of the
methods generally known for block polymerizations. The present
invention includes as an embodiment a thermoplastic copolymer
composition, which may be either a di-block, tri-block copolymer,
tetra-block copolymer or multi-block composition. In the case of
the di-block copolymer composition, one block is the alkenyl
arene-based homopolymer block and polymerized therewith is a second
block of a controlled distribution copolymer of diene and alkenyl
arene. In the case of the tri-block composition, it comprises, as
end-blocks the glassy alkenyl arene-based homopolymer and as a
mid-block the controlled distribution copolymer of diene and
alkenyl arene. Where a tri-block copolymer composition is prepared,
the controlled distribution diene/alkenyl arene copolymer can be
herein designated as "B" and the alkenyl arene-based homopolymer
designated as "A". The A-B-A, tri-block compositions can be made by
either sequential polymerization or coupling. In the sequential
solution polymerization technique, the mono alkenyl arene is first
introduced to produce the relatively hard aromatic block, followed
by introduction of the controlled distribution diene/alkenyl arene
mixture to form the mid block, and then followed by introduction of
the mono alkenyl arene to form the terminal block. In addition to
the linear, A-B-A configuration, the blocks can be structured to
form a radial (branched) polymer, (A-B).sub.nX, or both types of
structures can be combined in a mixture. In addition it is
contemplated that asymmetrical, polymodal block copolymers are
included, where some of the A blocks have higher molecular weights
than some of the other A blocks--e.g., such a polymer could have
the structure (A.sub.1-B).sub.d-X-.sub.e(B-A.sub.2) where d is 1 to
30 and e is 1 to 30, and the molecular weight of A1 and A2 blocks
differ by at least 20 percent. Some A-B diblock polymer can be
present but preferably at least about 70 weight percent of the
block copolymer is A-B-A or radial (or otherwise branched so as to
have 2 or more terminal resinous blocks per molecule) so as to
impart strength.
Preparation of radial (branched) polymers requires a
post-polymerization step called "coupling". In the above radial
formula n is an integer of from 2 to about 30, preferably from
about 2 to about 15, and X is the remnant or residue of a coupling
agent. A variety of coupling agents are known in the art and
include, for example, dihalo alkanes, silicon halides, siloxanes,
multifunctional epoxides, silica compounds, esters of monohydric
alcohols with carboxylic acids, (e.g. dimethyl adipate) and
epoxidized oils. Star-shaped polymers are prepared with polyalkenyl
coupling agents as disclosed in, for example, U.S. Pat. Nos.
3,985,830; 4,391,949; and 4,444,953; Canadian Patent Number
716,645. Suitable polyalkenyl coupling agents include
divinylbenzene, and preferably m-divinylbenzene. Preferred are
tetra-alkoxysilanes such as tetra-ethoxysilane (TEOS), aliphatic
diesters such as dimethyl adipate and diethyl adipate, and
diglycidyl aromatic epoxy compounds such as diglycidyl ethers
deriving from the reaction of bis-phenol A and epichirohydrin.
Additional possible post-polymerization treatments that can be used
to further modify the configuration of the polymers and therefore
their properties include capping and chain-termination. Capping
agents, such as ethylene oxide, carbon dioxide, or mixtures thereof
serve to add functional groups to the chain ends, where they can
then serve as reaction sites for further property-modifying
reactions. In contrast, chain termination simply prevents further
polymerization and thus prevents molecular weight growth beyond a
desired point. This is accomplished via the deactivation of active
metal atoms, particularly active alkali metal atoms, and more
preferably the active lithium atoms remaining when all of the
monomer has been polymerized. Effective chain termination agents
include water; alcohols such as methanol, ethanol, isopropanol,
2-ethylhexanol, mixtures thereof and the like; and carboxylic acids
such as formic acid, acetic acid, maleic acid, mixtures thereof and
the like. See, for example, U.S. Pat. No. 4,788,361, the disclosure
of which is incorporated herein by reference. Other compounds are
known in the prior art to deactivate the active or living metal
atom sites, and any of these known compounds may also be used.
Alternatively, the living copolymer may simply be hydrogenated to
deactivate the metal sites.
The polymerization procedures described hereinabove, including
preparation of the diene/alkenyl arene copolymer and of di-block
and multi-block copolymers prepared therewith, can be carried out
over a range of solids content, preferably from about 5 to about 80
percent by weight of the solvent and monomers, most preferably from
about 10 to about 40 weight percent. For high solids
polymerizations, it is preferable to add any given monomer, which
may include, as previously noted, a previously prepared homopolymer
or copolymer, in increments to avoid exceeding the desired
polymerization temperature. Properties of a final tri-block polymer
are dependent to a significant extent upon the resulting alkenyl
content and diene content. It is preferred that, to ensure
significantly elastomeric performance while maintaining desirably
high Tg and strength properties, as well as desirable transparency,
the tri-block and multi-block polymer's alkenyl arene content is
greater than about 20% weight, preferably from about 20% to about
80% weight. This means that essentially all of the remaining
content, which is part of the diene/alkenyl arene block, is
diene.
It is also important to control the molecular weight of the various
blocks. For an AB diblock, desired block weights are 3,000 to about
60,000 for the mono alkenyl arene A block, and 30,000 to about
300,000 for the controlled distribution conjugated diene/mono
alkenyl arene B block. Preferred ranges are 5000 to 45,000 for the
A block and 50,000 to about 250,000 for the B block. For the
triblock, which may be a sequential ABA or coupled (AB).sub.2 X
block copolymer, the A blocks should be 3,000 to about 60,000,
preferably 5000 to about 45,000, while the B block for the
sequential block should be about 30,000 to about 300,000, and the B
blocks (two) for the coupled polymer half that amount. The total
average molecular weight for the triblock copolymer should be from
about 40,000 to about 400,000, and for the radial copolymer from
about 60,000 to about 600,000. For the tetrablock copolymer ABAB
the block size for the terminal B block should be about 2,000 to
about 40,000, and the other blocks may be similar to that of the
sequential triblock copolymer. These molecular weights are most
accurately determined by light scattering measurements, and are
expressed as number average molecular weight.
An important feature of the thermoplastic elastomeric di-block,
tri-block and tetra-block polymers, including one or more
controlled distribution diene/alkenyl arene copolymer blocks and
one or more mono alkenyl arene blocks, is that they have at least
two Tg's, the lower being the single Tg of the controlled
distribution copolymer block which is an intermediate of its
constituent monomers' Tg's. Such Tg is preferably at least about
-60 degrees C., more preferably from about -40 degrees C. to about
+30 degrees C., and most preferably from about -40 degrees C. to
about +10 degrees C. The second Tg, that of the mono alkenyl arene
"glassy" block, is preferably from about +80 degrees C. to about
+110 degrees C., more preferably from about +80 degrees C. to about
+105 degrees C. The presence of the two Tg's, illustrative of the
microphase separation of the blocks, contributes to the notable
elasticity and strength of the material in a wide variety of
applications, and its ease of processing and desirable melt-flow
characteristics.
It should be noted that, in yet another embodiment, additional
property improvements of the compositions hereof can be achieved by
means of yet another post-polymerization treatment, that of
hydrogenation of the block copolymer. The preferred hydrogenation
is selective hydrogenation of the diene portions of the final block
copolymer. Alternatively both the B blocks and the A blocks may be
hydrogenated, or merely a portion of the B blocks may be
hydrogenated. Hydrogenation generally improves thermal stability,
ultraviolet light stability, oxidative stability, and, therefore,
weatherability of the final polymer. A major advantage is that the
distribution agent, such as the non-chelating monoether, which is
present during the initial polymerization process, does not
interfere with or otherwise "poison" the hydrogenation catalyst,
and thus the need for any additional removal steps is obviated.
Hydrogenation can be carried out via any of the several
hydrogenation or selective hydrogenation processes known in the
prior art. For example, such hydrogenation has been accomplished
using methods such as those taught in, for example, U.S. Pat. Nos.
3,595,942; 3,634,549; 3,670,054; 3,700,633; and Re. 27,145, the
disclosures of which are incorporated herein by reference. These
methods operate to hydrogenate polymers containing aromatic or
ethylenic unsaturation and are based upon operation of a suitable
catalyst. Such catalyst, or catalyst precursor, preferably
comprises a Group VIII metal such as nickel or cobalt which is
combined with a suitable reducing agent such as an aluminum alkyl
or hydride of a metal selected from Groups I-A, II-A and III-B of
the Periodic Table of the Elements, particularly lithium, magnesium
or aluminum. This preparation can be accomplished in a suitable
solvent or diluent at a temperature from about 20.degree. C. to
about 80.degree. C. Other catalysts that are useful include
titanium based catalyst systems.
Hydrogenation can be carried out under such conditions that at
least about 90 percent of the conjugated diene double bonds have
been reduced, and between zero and 10 percent of the arene double
bonds have been reduced. Preferred ranges are at least about 95
percent of the conjugated diene double bonds reduced, and more
preferably about 98 percent of the conjugated diene double bonds
are reduced. Alternatively, it is possible to hydrogenate the
polymer such that aromatic unsaturation is also reduced beyond the
10 percent level mentioned above. Such exhaustive hydrogenation is
usually achieved at higher temperatures. In that case, the double
bonds of both the conjugated diene and arene may be reduced by 90
percent or more.
Once the hydrogenation is complete, it is preferable to extract the
catalyst by stirring with the polymer solution a relatively large
amount of aqueous acid (preferably 20 30 percent by weight), at a
volume ratio of about 0.5 parts aqueous acid to 1 part polymer
solution. Suitable acids include phosphoric acid, sulfuric acid and
organic acids. This stirring is continued at about 50.degree. C.
for about 30 to about 60 minutes while sparging with a mixture of
oxygen in nitrogen. Care must be exercised in this step to avoid
forming an explosive mixture of oxygen and hydrocarbons.
In an alternative, the block copolymer may be functionalized in a
number of ways. One way is by treatment with an unsaturated monomer
having one or more functional groups or their derivatives, such as
carboxylic acid groups and their salts, anhydrides, esters, imide
groups, amide groups, and acid chlorides. The preferred monomers to
be grafted onto the block copolymers are maleic anhydride, maleic
acid, fumaric acid, and their derivatives. A further description of
functionalizing such block copolymers can be found in Gergen et al,
U.S. Pat. No. 4,578,429 and in U.S. Pat. No. 5,506,299. In another
manner, the selectively hydrogenated block copolymer may be
functionalized by grafting silicon or boron containing compounds to
the polymer as taught in U.S. Pat. No. 4,882,384. In still another
manner, the block copolymer may be contacted with an alkoxy-silane
compound to form silane-modified block copolymer. In yet another
manner, the block copolymer may be functionalized by grafting at
least one ethylene oxide molecule to the polymer as taught in U.S.
Pat. No. 4,898,914, or by reacting the polymer with carbon dioxide
as taught in U.S. Pat. No. 4,970,265. Still further, the block
copolymers may be metallated as taught in U.S. Pat. Nos. 5,206,300
and 5,276,101, wherein the polymer is contacted with an alkali
metal alkyl, such as a lithium alkyl. And still further, the block
copolymers may be functionalized by grafting sulfonic groups to the
polymer as taught in U.S. Pat. No. 5,516,831. All of the patents
mentioned in this paragraph are incorporated by reference into this
application.
The last step, following all polymerization(s) as well as any
desired post-treatment processes, is a finishing treatment to
remove the final polymer from the solvent. Various means and
methods are known to those skilled in the art, and include use of
steam to evaporate the solvent, and coagulation of the polymer
followed by filtration. The final result is a "clean" block
copolymer useful for a wide variety of challenging applications,
according to the properties thereof. These properties include, for
example, the final polymer's stress-strain response, which shows
that a composition exhibits a stiffer rubbery response to strain,
therefore requiring more stress to extend the same length. This is
an extremely useful property that allows the use of less material
to achieve the same force in a given product. Elastic properties
are also modified, exhibiting increasing modulus with increasing
elongation, and there is a reduced occurrence of the rubbery
plateau region where large increases in elongation are required to
procure an increase in stress. Another surprising property is
increased tear strength. The controlled distribution copolymers
offer additional advantage in their ability to be easily processed
using equipment generally designed for processing thermoplastic
polystyrene, which is one of the most widely known and used alkenyl
arene polymer. Melt processing can be accomplished via extrusion or
injection molding, using either single screw or twin screw
techniques that are common to the thermoplastics industry. Solution
or spin casting techniques can also be used as appropriate.
In the U.S. Pat. No. 5,516,831 to Pottick, et al. ('831), it is
taught to sulfonate a block copolymer. Therein it is disclosed that
hydrogenated block copolymers are sulfonated primarily in the
alkenyl arene blocks by reaction with a sulfonation reagent that
selectively sulfonates the alkenyl arene blocks in preference to
the hydrogenated polydiene blocks. It is further disclosed therein
that acyl sulfates exhibit the desired preference for sulfonation
of the alkenyl arene blocks. The '831 reference teaches that acetyl
sulfate is the most preferred sulfonation reagent. Acetyl sulfate
(CH.sub.3CO.sub.2--SO.sub.3H) should be prepared fresh before each
sulfonation reaction or prepared in situ by the reaction of acetic
anhydride with sulfuric acid. While the reaction of sulfuric acid
and acetic anhydride is the preferred method of preparing the
acetyl sulfate, any method known to those of ordinary skill in the
art of preparing acetyl sulfate to be useful can be used with the
method.
The sulfonated polymers are preferably prepared with about one (1)
sulfonic acid or sulfonate group per aromatic ring. Preferably, the
functionality level is on the average from about one (1) functional
group per molecule of the copolymer to about one functional group
per aromatic ring, and more preferably on the average from about
three (3) functional groups per molecule of the copolymer to about
one (1) functional group per two aromatic rings of the
molecule.
The sulfonated polymers can be prepared wherein there are
additional groups between the sulfonic acid group and the aromatic
ring of the block copolymer. For example, the copolymers can have
the general formula: --Ar(X)-- wherein Ar is an aromatic ring of
the block copolymer and X is --SO.sub.3H or
--P(O)(OR.sup.8)O--R.sup.9--SO.sub.3H where R.sup.8 is hydrogen or
lower alkyl and R.sup.9 is lower alkylene. Preferably the sulfonic
acid group is bonded directly to the aromatic ring but these and
obvious variations of this general formula are also within the
scope. The sulfonated block copolymers can also be prepared by
grafting a sulfonated polymer to a block copolymer through, for
example, reaction with residual unsaturation in the block
copolymer.
The sulfonated block copolymers can be prepared in either a batch
process or a continuous process. In a batch process, to achieve
high levels of sulfonation, it can be desirable to balance both the
solubility of the sulfonated polymer and the temperature of the
reaction. The unsulfonated block copolymers are relatively soluble
in solvents, such as dichloroethane. As sulfonation occurs, the
sulfonated polymer can become progressively more insoluble.
Solubility of the polymer in the solvent often cannot be controlled
by raising the reaction temperature because excessive temperature
can cause crosslinking and other undesirable effects in the product
sulfonated block copolymers. In order to avoid these problems, it
can be desirable to run the sulfonation at a temperature that is
high enough to ensure reasonable solubilities while not exceeding
temperatures at which undesirable effects occur with the polymer.
This temperature range happens to be about the same for both batch
and continuous process and is from about 30.degree. C. to about
70.degree. C., preferably from about 35.degree. C. to about
55.degree. C., more preferably from about 38.degree. C. to about
50.degree. C., and most preferably about 50.degree. C.
In a batch process, it is generally desirable to run the reaction
with a polymer concentration of from about 1 to about 5 percent by
weight polymer in the solvent. More preferably, it is desirable to
run a batch process with a polymer concentration of from about 2 to
about 4 percent by weight polymer in the solvent. Most preferably
it is desirable to run a batch process with a polymer concentration
of 3 percent by weight polymer in the solvent.
In a continuous process it is generally desirable to run the
reaction with a polymer concentration of from about 0.1 to about 10
percent by weight polymer in the solvent. More preferably, it is
desirable to run a batch process with a polymer concentration of
from about 0.5 to about 2.5 percent by weight polymer in the
solvent. Most preferably it is desirable to run a batch process
with a polymer concentration of 2 percent by weight polymer in the
solvent.
For a typical continuous process, the polymer is dissolved in a
solvent, preferably a chlorinated hydrocarbon, nitro hydrocarbon,
fluorinated hydrocarbon, or supercritical carbon dioxide.
Temperature of the polymer solution is reduced to -5.degree. C. to
15.degree. C. The sulfonate reactant is prepared by vaporization of
SO.sub.3 and dilution to a low concentration level in a gas, such
as dry air, nitrogen or sulfur dioxide, or a solvent, such as a
chlorinated hydrocarbon, nitro hydrocarbon, fluorinated carbon,
supercritical carbon dioxide, or liquid sulfur dioxide. In one
embodiment, the solvent is 1,2-dichloroethane, methylene chloride,
chloroform, nitromethane, or a mixture thereof. The polymer
solution and SO.sub.3 reactant are subject to counter-flow in a
falling film reactor, keeping the polymer solution cold during the
reaction process. Unreacted SO.sub.3 gas exiting the reactor is
collected and neutralized. Alternately, the polymer solution and
SO.sub.3 reactant are mixed in a high shear environment, keeping
the mixing time under one second. Ideally the mixing is done under
elevated pressure to keep the SO.sub.3 in solution. The output from
the mixing process is collected and the mixed solution is agitated
for an additional 120 seconds while holding the temperature at
-5.degree. C. to 15.degree. C. The sulfonated polymer
solution/suspension is collected and the solvent boiled off. In a
preferred embodiment, the process additionally comprises recovering
and reusing the solvent. Sulfur dioxide may replace air or nitrogen
as the carrier gas, especially for the case where sulfur trioxide
is prepared in-line by oxidation of sulfur dioxide.
While not wishing to be bound by any theory, it is believed that
the polymers lend themselves to sulfonation due to the presence of
aromatic groups within the midblocks of the copolymers. In a
conventional block copolymer, the solubility of the polymer is
affected by the substantial absence of aromatic groups in the
midblock. The aromatic groups in the midblock allow the copolymers
to stay soluble further into the reaction allowing for additional
sulfonation of the molecules. For a batch process, for example, a
block copolymer having about 64 percent by weight styrene groups
can have a sulfonation content of from about 25 to about 70
percent. For a continuous process, for example, a block copolymer
have about 64 percent by weight styrene groups can have a
sulfonation content of from about 25 to about 70 percent. In a
preferred embodiment the level of sulfonation should be about 30 to
40 mol percent, basis the styrene content of the polymer where the
overall styrene content of the polymer is about 60 to about 70
weight percent, and the A blocks of the block copolymer have a
number average molecular weight of about 10.000 to about
35,000.
The polymer is dissolved in a solvent as part of the process of
performing the sulfonation. Preferably the solvent is a
hydrocarbon, nitro hydrocarbon, or chlorinated hydrocarbon. In one
embodiment, the sulfonation process is carried out in a solvent
selected from the group consisting of 1,2-dichloroethane,
trichlorobenzene, chlorobenzene, methylene chloride, chloroform and
mixtures thereof. In another embodiment, the solvent is selected
from the group consisting of cyclohexane, heptane, octane,
nitrobenzene, nitropropane and mixtures thereof.
While the process described above is the preferred process for
preparing the sulfonated copolymers, these materials can be
prepared by conventional methods as well. For example, the
copolymers can be sulfonated by heating the polymer in sulfuric
acid, preferably using silver sulfate as a catalyst. Complexes with
a number of agents such as phosphorus pentoxide, triethyl phosphate
and tris (2-ethylhexyl) phosphatecan be used to modulate i.e.,
moderate the reactivity of sulfur trioxide. Other acyl sulfates,
formed by premixing can be used and include, sulfur trioxide/acetic
acid, sulfur trioxide/lauric acid, and chlorosulfonic acid/lauric
acid. In addition, chlorosulfonic acid and trimethylsilyl-sulfonyl
chloride have been found useful. In one embodiment, methylene units
are readily inserted between the sulfonate group and the phenyl
group by first carrying out an acylation of the ring with and
.alpha.,.omega.-acyl/alkyl dichloride of desired carbon length and
then transforming the chloride into the sulfonate. Similarly,
cyclic sulfonyl esters known as sultones may be used to avoid the
transformation step A unique route to sulfonated polymers is the
use of sulfur dioxide and chorine gas. In still another embodiment,
it is possible to first sulfonate the monomers then carry out the
polymerization. The sulfonated monomers (protonic form) are
sometimes polymerized in the sodium salt form or can be protected
by forming the sulfonyl ester and then polymerized. Ion exchange or
hydrolysis follows to obtain the protonic form of the polymer.
A sulfonation process for styrene copolymers is described in U.S.
Pat. Nos. 5,468,574, 5,679,482, and 6,110,616. The preferred level
of sulfonic acid functionality ranges from about one functional
group per five aromatic rings (20 mol %) to about four functional
groups per five aromatic rings (80 mol %), such that the equivalent
weight of the resulting sulfonated polymer is from about 100
grams/sulfonate equivalent to about 1000 grams/sulfonate
equivalent. For example, for a copolymer of 45 weight percent
styrene, the preferred range is between one sulfonic acid group per
five styrene units (20 mol %, equivalent weight=1200
grams/equivalent) to about four sulfonic acid group per five
styrene units (80 mol %, equivalent weight=300 grams/equivalent).
Equivalent weight may be further limited to 400 700, and even
further limited to 520 690. For a copolymer of 30 weight percent
styrene, the preferred range is between one sulfonic acid group per
four styrene units (25 mol %, equivalent weight=1400
grams/equivalent) to four sulfonic acid groups per five styrene
units (80 mol %, equivalent weight=430 grams/equivalent). The
sulfonation level of the polymer may be controlled by the
stoichiometric ratio of the sulfonating agent, acetyl sulfate, to
the styrene content of the polymer. For example, addition of 1.0
equivalents of acetyl sulfate yields a polymer of 32 mol %
sulfonation and 1.4 equivalents yields 44 mol % sulfonation. The
resulting polymer possesses a low equivalent weight, from 1000 down
to 100, preferably 700 down to 300 and most preferably 690 down to
380.
A sol-gel process using an alkoxy silane and incorporating a host
polymer has been described in the literature. A polymer such as
Nafion.RTM. perflorinated ionomer was swollen with solvent and then
immersed in a solution of solvent, water, acid and alkoxidesilicate
such tetraethylorthosilicate (TEOS) or vinyltriethoxysilane (VTES).
TEOS or VTES and its hydrolyzed species diffused into the hose
polymer and reacted to form silicate particles while the solvent
was removed under heat/vacuum.
An improved process is to prepare the hybrids by forming the
nanocomposite in a single major step as the polymer forms a film,
and the co-dissolved in organic alkoxide, such as TEOS or VTES
undergoes a sol-gel reaction, simultaneously forming a solution.
This method is inherently simpler than the previous since polymer
film does not have to be preformed before an in situ sol-gel
reaction. Moreover, this method gives better control over how much
silicate is incorporated into the polymer matrix. The previous
method relied upon how much TEOS precursor could diffuse into the
matrix in a given time, whereas silicate uptake is now controlled
by how much precursor is charged into the polymer solution.
The micro- and macrostructure of the polymer matrix can be
controlled through the optimization of several parameters, for
example, coupling agents (different Si, Ti, Al, Zr, and B), pH,
concentration, temperature, and solvent.
DEFINITIONS
Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of a
straight, branched, cyclic configuration and combinations thereof
attached to the parent structure through an oxygen. Examples
include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, and
cyclohexyloxy. Lower alkoxy refers to groups containing one to four
carbonsAcyl refers to groups of from 1 to 8 carbon atoms of a
straight, branched, cyclic configuration, saturated, unsaturated
and aromatic and combinations thereof, attached to the parent
structure through a carbonyl functionality. One or more carbons in
the acyl residue may be replaced by nitrogen, oxygen or sulfur as
long as the point of attachment to the parent remains at the
carbonyl. Examples include acetyl, benzoyl, propionyl, isobutyryl,
t-butoxycarbonyl, and benzyloxycarbonyl. Lower-acyl refers to
groups containing one to four carbons.
Aryl and heteroaryl mean a 5- or 6-membered aromatic or
heteroaromatic ring containing 0 3 heteroatoms selected from
nitrogen, oxygen or sulfur; a bicyclic 9- or 10-membered aromatic
or heteroaromatic ring system containing 0 3 heteroatoms selected
from Nitrogen, oxygen or sulfur; or a tricyclic 13- or 14-membered
aromatic or heteroaromatic ring system containing 0 3 heteroatoms
selected from Nitrogen, oxygen or sulfur. Each of these rings is
optionally substituted with 1 3 lower alkyl, substituted alkyl,
substituted alkynyl, carbonyl, nitro, halogen, haloalkyl, hydroxy,
alkoxy, OCH(COOH).sub.2, cyano, primary amino, secondary amino,
acylamino, phenyl, benzyl, phenoxy, benzyloxy, heteroaryl, or
heteroaryloxy; each of said phenyl, benzyl, phenoxy, benzyloxy,
heteroaryl, and heteroaryloxy is optionally substituted with 1 3
substitutents selected from lower alkyl, alkenyl, alkynyl, halogen,
hydroxy, haloalkyl, alkoxy, cyano, phenyl, benzyl, benzyloxy,
carboxamido, heteroaryl, heteroaryloxy, nitro or --NRR (wherein R
is independently H, lower alkyl or cycloalkyl, and --RR may be
fused to form a cyclic ring with nitrogen). The aromatic 6- to
14-membered carbocyclic rings include, for example, benzene,
naphthalene, indane, tetralin, and fluorene; and the 5- to
10-membered aromatic heterocyclic rings include, e.g., imidazole,
pyridine, indole, thiophene, benzopyranone, thiazole, furan,
benzimidazole, quinoline, isoquinoline, quinoxaline, pyrimidine,
pyrazine, tetrazole and pyrazole.
Alkylaryl means an alkyl residue attached to an aryl ring. Examples
are benzyl and phenethyl. Heteroarylalkyl means an alkyl residue
attached to a heteroaryl ring. Examples include pyridinylmethyl and
pyrimidinylethyl.
Heterocycle means a cycloalkyl or aryl residue in which one to two
of the carbons is replaced by a heteroatom such as oxygen, nitrogen
or sulfur. Examples of heterocycles that fall within the scope of
the invention include pyrrolidine, pyrazole, pyrrole, indole,
quinoline, isoquinoline, tetrahydroisoquinoline, benzofuran,
benzodioxan, benzodioxole (commonly referred to as
methylenedioxyphenyl, when occurring as a substituent), tetrazole,
morpholine, thiazole, pyridine, pyridazine, pyrimidine, thiophene,
furan, oxazole, oxazoline, isoxazole, dioxane, and
tetrahydrofuran.
Substituted alkyl, aryl, cycloalkyl, or heterocyclyl refer to
alkyl, aryl, cycloalkyl, or heterocyclyl wherein up to three H
atoms in each residue are replaced with halogen, haloalkyl,
hydroxy, lower alkoxy, carboxy, carboxalkoxy, carboxamido, cyano,
carbonyl, nitro, primary amino, secondary amino, alkylthio,
sulfoxide, sulfone, acylamino, acyloxy, amidino, phenyl, benzyl,
heteroaryl, phenoxy, benzyloxy, heteroaryloxy, or substituted
phenyl, benzyl, heteroaryl, phenoxy, benzyloxy, or
heteroaryloxy.
Haloalkyl refers to an alkyl residue, wherein one or more H atoms
are replaced by halogen atoms; the term haloalkyl includes
perhaloalkyl. Examples of haloalkyl groups that fall within the
scope of the invention include CH.sub.2F, CHF.sub.2, and
CF.sub.3.
The humidity-conducting polymer may contain one or more additives,
including flame retardants (suppressants and synergists), biocides
(mildewicides, fungicides, anti-mold agents, antiviral agents,
bacteriocides, anti-parasitic agents, and insecticides.),
plasticizers, uv stabilizers (uv absorbers, and light stabilizers),
antioxidants (primary or secondary) and thermal stabilizers. Any
one compound may impart one or more characteristic enhancements.
The basic requirements are that (a) the additive is miscible with
the hydrophilic polymer, (b) it does not compromise the mechanical
strength or integrity of the membrane in the cell, (c) it not
reduce the performance (e.g. moisture transfer effectiveness) or
lifetime of the cell in the application. Therefore, these are
objects (a, b, c) of the invention. Although not an object, it is
desirable that the additive, retain the activity and efficacy of
said characteristic when present with the polymer in the
formulation.
For biocides, a principal concern is mold and mildew growth because
of the potentially low, local pH of these sulfonated hydrophilic
polymers. However, resistance to other possible biological agents
such as fungus, bacteria, viruses, parasites, insects or protozoa
is desirable. Any biologicals that reduce the available surface
area of the membrane for transfer of moisture from the stream must
be prevented. Compatible chemical agents are
10,10'-oxybisphenoxarsine available from Rohm and Haas in a liquid
or resin carrier under the tradname Vinyzene. An arsenic-free
alternative is 4-chloro-3,5-dimethyl phenol an organic chemical
available from Aldrich. These can be used effectively at loadings
up to 5.0 phr. However, Dow Chemical's fungicide AMICAL 48 and
bactericide BIOPAN BP PLUS, both toxic metal-free are
preferred.
Flame retardancy is important insofar as additives can reduce the
tendency of the cell to catch fire, spread a fire and to reduce
smoke emissions. For pure liquid streams the threat of fire does
not present itself, except for air/water or some other highly polar
gas vapor streams at low humidity. For these applications, a
non-halogen flame retardant (basically a flame inhibitor) is
typically used for polyolefins. This is available from Unitex
chemical under the tradename Uniplex FRX 44-94S. Bromine-containing
retardants, Uniplex BAP-755 (brominated alkyl phosphate) and
Uniplex FRP-64 (poly (2,6-dibromophenylene oxide)) are also viable.
For high performance, the polymeric, flame retardant is desirable
but it requires a synergist, for which the high
phosphorous-containing FRX 44-94S is suitable. However, Great Lakes
Chemicals' tetrabromobisphenol A is preferred for polymer
solubility.
Organophosphates serve as hydrophilic plasticizers that function by
increasing the water or some other highly polar liquid retention of
the membrane in HUX cell in the application environment. The
increased water or some other highly polar liquid content may
improve performance by increasing membrane permeability as well as
reduce flammability, since substantially more water or some other
highly polar liquid must evaporate before flames may spread to the
cell. In the process, the evaporation of water or some other highly
polar liquid suppresses smoke. Also, these can potentially function
as synergists for bromine-containing flame retardants. These are
trialkyl phosphates, such as trimethyl phosphate, triethyl
phosphate, tripropyl phosphate and tris(2-ethyl hexyl)
phosphate.
Antioxidants (and thermal stabilizers) can increase shelf life of
HUX cells by circumventing the auto-oxidation of the hydrophilic
polymer during storage. However, a more important advantage is the
ability to reduce oxidation of the sulfonated hydrophilic polymer
in the HUX cell during operation since at low humidity the polymer
is continuously subject to the transfer of heat and thus, will see
temperatures as high as 37.degree. C. Oxidation of organic
impurities may result and reduce performance this be minimized with
the use of antioxidants. These are basically hindered phenols of
high molecular weight and include:
stearyl-3-(3',5'-di-tert-butyl-4-hydroxyphenyl) propionate (BNX
1076) and tetrakis[methylene-3
(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate] methane (BNX 1010)
both available from Mayo Corp. and poly(phenol-formaldehyde)
novalac resin (HRJ-12700) available from Schenectady International.
Peroxide decomposers add benefit as synergists to hindered phenols,
these are aryl phosphites; such as Tris(2,4-ditert-butylphenyl)
phosphite (Benafos 1680). UV stabilizers are important for outdoor
applications; these are light absorbers with a broad absorption
range of which benzotriazoles are preferred. Ciba's Tinuvin 384-2
(Benzene propionic acid
(3-2H-benzotriazol-2-yl)-5-(1,1-di-methylethyl-4)-hydroxy,
C.sub.7-C.sub.9-branched and linear alkyl esters) is suitable
because of good thermal and environmental stability. Hindered amine
light stabilizers (HALS) may be suitable. However, free amines form
salts that may reduce water or some other highly polar liquid
transport, these are less preferred. Therefore, nitroso-alkyl and
specifically nitroso-alkyl ethers containing HALS are preferred for
these polymers to maximize their effectiveness as stabilizers.
The HUX support material is preferably, but not limited to, a
polyolefin, spaced-member, fiber netting. Fiber extrusion followed
by melt bonding is a common method to prepare the netting, however,
other methods can be used by themselves or in combination. These
include injection molding, compression molding, fiber extrusion
with solvent bonding, spin bonding, and ultrasonic welding.
Suitable materials for reinforcing substrate 14 include woven,
nonwoven, knit and cross-laid fabrics; in the context of the
present invention, the term `fabrics` is defined as including
meshes and nettings. Microporous films may also be used. The fabric
of a reinforcing substrate may be composed of synthetic fibers or
filaments, glass yarns, non-corroding metal fibers, such as nickel
fibers, or carbon fibers. The fibers, filaments or yarns should be
ones to which the water-conducting polymer film adheres strongly.
Suitable synthetic fibers include polyolefins, particularly
polyethylene or polypropylene, and polyesters. The fibers may have
organic or inorganic sizing agents or coupling agents applied,
including polyvinylalcohol, starches, oil, polyvinylmethylether,
acrylic, polyester, vinylsilane, aminosilane, titanate, and
zirconate. Silicone-based lubricants are sometimes employed for
greater tear strength. A microporous film may be composed of any
synthetic polymer to which the humidity-conducting polymer adheres.
In particular, the films may have a polyolefin composition, and
more particularly, polyethylene. Films having a fluoropolymer
composition may also be used. A membrane according to the present
invention may be prepared by impregnating the substrate with a
humidity-conducting polymer. This may be done by any of several
known methods. These methods include direct coating, wherein a
solution of the humidity-conducting polymer in a suitable solvent,
such as a lower alcohol, in particular, methanol or propanol. The
benefit of direct coating is that it reduces the number of
sub-assemblies and parts and, thus, reduces costs. Low cost
fabrication is an object of the invention. Indirect coating
methods, such as solution casting, may also be used.
Sequential buildup facilitates the manufacturing of the overall
composite; coating is typically continued until a homogenous sheet
is formed when reinforcement may or may not be completely coated.
Formulations that readily wet the substrate are available at low
cost and produce composites without holes or other defects are
preferred. Alternatively, the water-conducting polymer may be
applied to the reinforcing substrate by hot roll laminating it with
reinforcing substrate, thus eliminating the need for multiple
coating passes. The water-conducting polymer film may also contain
a ceramic filler, if desired. Finally, a membrane composed of
nonwoven fabric may be manufactured by adding staple-pulped fiber
to solution of the water conducting polymer, and coating on a
release substrate.
Micro-reinforced composites can benefit from crosslinking
chemistries described as well. These are microporous supports those
that have pore sizes less than a few microns and exceptionally
large open volumes greater than 70%, and a thickness of less than a
mil, fabricated from mostly polyolefins; polyethylene (high density
or ultra high molecular weight) and propylene, but
polytetrafluoroethylene is very common, polyester and polyamide to
a lesser extent. In the process, the polymer is impregnated into
the support but any number of processes; solution casting, melt
impregnation, using a knife blade, knife-over-roll, reverse-roll
and others. The polymer electrolyte is crosslinked within the
support and depending on the chemistry may be grafted to the
support to some extent. The micro-reinforced polymer electrolyte
membrane is substantially stronger and if impregnated properly has
vastly reduced water uptake and thus, improved dimensional
stability than the crosslinked PEM alone. The one challenge is that
if sufficient grafting of the PEM to the reinforcement is not
achieved these materials can exhibit interfacial failure when
hydration cycled in the application. So proper choice of initiator
and coupling agent is necessary for maximum benefit. Pretreatment
of the reinforcement beforehand to introduce functional groups on
the surfaces is important for maximum adhesive strength. In the
context of the present invention, alkyl is intended to include
linear, branched, or cyclic hydrocarbon structures and combinations
thereof. Lower alkyl refers to alkyl groups of from 1 to 4 carbon
atoms. Lower alkyl groups include methyl, ethyl, n-propyl,
isopropyl, and n-, s- and t-butyl. Preferred alkyl groups are those
of C.sub.20 or below. Cycloalkyl is a subset of alkyl and includes
cyclic hydrocarbon groups of from 3 to 8 carbon atoms. Examples of
cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and
norbornyl.
FIG. 2 is a partially exploded view of a humidity exchange cell or
ventilator core 20 including a hydrophilic organic-inorganic hybrid
membrane 10, a first chamber 22 for containing a first fluid, a
second chamber 24 for containing a second fluid and a number of
spacers or ribs 16 which are adhered to membrane 10. Cell 20
includes a series of alternating first and second chambers. A cap
26 may be used to enclose the topmost and/or bottommost
chambers.
The membranes 10 are stacked one on top of another to form
ventilator core 20 as shown in FIG. 2. The orientation of the each
layer is rotated by 90 degrees as it is put down into the core.
This forms the cross-flow pattern for the exchange of heat, ions
and/or moisture within the core. Not shown, but fully realizable,
is a counter-flow arrangement of the layers. Here the layers would
be in a single orientation, with no rotation, in the core. A
complex manifold would be designed to route gas streams to every
other layer in the stack. These manifolds would be placed on
opposite sides of the core. The non-manifolded sides of the core
could be sealed to the external environment if necessary.
Spacer 16, as shown in FIGS. 1 and 2, is configured as a series of
ribs, typically adhered to the humidity-conducting polymer surface.
These ribs may have a synthetic polymer composition, particularly,
PVC, and may be rectangular or circular in cross-section. In other
embodiments (not shown), spacer 16 may be a corrugated paper or
plastic sheet. In some embodiments, spacer 16 may be a series of
adhesive beads. The adhesive may be a hot-melt, cold-melt, or solid
adhesive; it may be either thermoplastic or thermosetting. The HUX
cell may possess certain specific sub-elements to be effective as a
mass (i.e. moisture) exchanger. The basic sub-elements are as
follows: (a) a hydrophilic organic-inorganic hybrid membrane
formulated to be highly permeable to water or some other highly
polar liquid or gas, (b) a support matrix to impart mechanical
integrity to the membrane and to maintain planarity during
operation and (c) a manifold for the distribution of a fluid across
the face of the membrane. The disclosed HUX cell is of unitary
design in that it incorporates all three sub-elements into a
complete cell structure that can be fabricated as a single unit.
The device can be built up of this structure by simple stacking and
securing the cells in an enclosure.
The organic-inorganic hybrids of the present invention can be used
in many applications, such as in Fuel Cells as an electrolyte;
Water Electrolyzers as an electrolyte; Acid Electrolyte Battery
Electrolyte Separators; Super-Capacitors Electrolytes; Separation
Cell Electrolyte Barriers for Metal Recovery Processes; and the
like. These applications are described in more detail in U.S. Pat.
Nos. 5,468,574; 5,679,482; 5,677,074 and 6,110,616, to Dais
Analytic Corporation. The hybrids may also be used as moisture
transfer agents. These materials are useful in High Volume Air
Conditioning (HVAC); Low Temperature Distillation Membranes for
Desalination; Prevaporation (Industrial Gas Modification and
Clean-up); Air Moisture Removal/Augmentation for Industrial
Processes, Medical Applications, Building Environments (Permeable
Wall Coatings), and Tents or Temporary Enclosures. These
applications are described in more detail in U.S. Pat. Nos.
6,413,298, 6,383,391, 5,840,387 and 6,306,419; and published U.S.
Patent Application Nos. 20030106680 and 20030118887 to Dais
Analytic Corporation.
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